Ricoh VT3500, Service Manual

Page: 175 / 330

9.4.4 Thermal Head Protection
A thermistor on the thermal head and a thermal guard (a thermostat) on the
power supply unit are used for thermal head protection. This prevents the
thermal head and power supply unit from overheating when continuously
processing a solid image. The CPU detects the abnormal condition and lights
the SC code on the operation panel as follows:
Detecting Component Detecting Temperature Signal Level SC Code
Thermistor 54°C 1.17 V CN109-A8 E-04
Thermistor Under 54°C Over 1.17 V Recovery
Thermal Guard 85°C 0 V CN107-9 E-08
Thermal Guard Under 85°C 5 V Recovery
The CPU also lights SC code in the following conditions:
Conditions Possible Cause SC Code
The signal level
between CN109-A8
and GND is over
4.9 volts. 1) Thermistor open. E-09
2) Related connectors are not connected.
(See the above figure.)
+5
CN404-b8
CN109-A8
CN705-22
CN403-22 CN703-10
CN502-10
CN107-9
+5
CPU
Thermal Head
Thermal Head
Drive PCB Image Processing
PCB
Main PCB PSU
Thermistor
Thermal
Guard
1 December 1993
2-139